In this paper, I will try to examine from both philosophical and epistemological points of view the major developments of neurophysiological research on sleep and dreaming during the last sixty years. In the nineteen fifties and sixties, neurophysiologists and psychophysiologists had great hopes regarding the contribution of sleep and dreaming studies to the understanding of consciousness mechanisms. These hopes were not entirely fulfilled. Progress in the field of sleep research was achieved thanks to developments in disciplines like neurophysiology properly said, neurochemistry, clinical medicine, etc